Bump min supported chrome version from 71 -> 73

This means we no longer need to worry about engines without mutable
global support.

Followup to #25375.

Author: sbc100

site/source/docs/tools_reference/settings_reference.rst

@@ -2897,7 +2897,7 @@ This setting also applies to modern Chromium-based Edge, which shares version
 numbers with Chrome.
 Chrome 85 was released on 2020-08-25.
 MAX_INT (0x7FFFFFFF, or -1) specifies that target is not supported.
-Minimum supported value is 71, which was released on 2018-12-04 (see
+Minimum supported value is 74, which was released on 2019-04-23 (see
 feature_matrix.py).
 
 Default value: 85

src/settings.js

@@ -1901,7 +1901,7 @@ var MIN_SAFARI_VERSION = 150000;
 // numbers with Chrome.
 // Chrome 85 was released on 2020-08-25.
 // MAX_INT (0x7FFFFFFF, or -1) specifies that target is not supported.
-// Minimum supported value is 71, which was released on 2018-12-04 (see
+// Minimum supported value is 74, which was released on 2019-04-23 (see
 // feature_matrix.py).
 // [link]
 var MIN_CHROME_VERSION = 85;

tools/feature_matrix.py

@@ -22,7 +22,7 @@
 
 # N.b. when modifying these values, update comments in src/settings.js on
 # MIN_x_VERSION fields to match accordingly.
-OLDEST_SUPPORTED_CHROME = 71  # Released on 2018-12-04
+OLDEST_SUPPORTED_CHROME = 74  # Released on 2019-04-23
 OLDEST_SUPPORTED_FIREFOX = 65  # Released on 2019-01-29
 OLDEST_SUPPORTED_SAFARI = 120200  # Released on 2019-03-25
 # 12.22.09 is the oldest version of node that we do any testing with.
@@ -34,7 +34,6 @@ class Feature(IntEnum):
   NON_TRAPPING_FPTOINT = auto()
   SIGN_EXT = auto()
   BULK_MEMORY = auto()
-  MUTABLE_GLOBALS = auto()
   JS_BIGINT_INTEGRATION = auto()
   THREADS = auto()
   PROMISE_ANY = auto()
@@ -63,12 +62,6 @@ class Feature(IntEnum):
     'safari': 150000,
     'node': 130000,
   },
-  Feature.MUTABLE_GLOBALS: {
-    'chrome': 74,
-    'firefox': 61,
-    'safari': 120000,
-    'node': 120000,
-  },
   Feature.JS_BIGINT_INTEGRATION: {
     'chrome': 67,
     'firefox': 68,